[PATCH] c++ modules: ICE with templated friend and std namespace [PR100134]

[Patrick Palka <ppalka@redhat.com>]

IIUC the function depset::hash::add_binding_entity has an assert
verifying that if a namespace contains an exported entity, then
the namespace must have been opened in the module purview:

  if (data->hash->add_namespace_entities (decl, data->partitions))
    {
      /* It contains an exported thing, so it is exported.  */
      gcc_checking_assert (DECL_MODULE_PURVIEW_P (decl));
      DECL_MODULE_EXPORT_P (decl) = true;
    }

We're tripping over this assert in the below testcase because by
instantiating and exporting std::A<int>, we end up in turn defining
and exporting the hidden friend std::f without ever having opening
the enclosing namespace std within the module purview and thus
DECL_MODULE_PURVIEW_P (std_node) is false.

Note that it's important that the enclosing namespace is std here: if we
use a different namespace then the ICE disappears.  This probably has
something to do with the fact that we predefine std via push_namespace
from cxx_init_decl_processing (which makes it look like we've opened the
namespace in the TU), whereas with another namespace we would instead
lazily obtain the NAMESPACE_DECL from add_imported_namespace.

Since templated frined functions are special in that they give us a way
to declare a new namespace-scope function without having to explicitly
open the namespace, this patch proposes to fix this issue by propagating
DECL_MODULE_PURVIEW_P from a friend function to the enclosing namespace
when instantiating the friend.

Tested on x86_64-pc-linux-gnu, does this look like the right fix?  Other
solutions that seem to work are to set DECL_MODULE_PURVIEW_P on std_node
after the fact from declare_module, or simply to suppress the assert for
std_node.

	PR c++/100134

gcc/cp/ChangeLog:

	* pt.cc (tsubst_friend_function): Propagate DECL_MODULE_PURVIEW_P
	from the new declaration to the enclosing namespace scope.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/tpl-friend-8_a.H: New test.
	* g++.dg/modules/tpl-friend-8_b.C: New test.
---
 gcc/cp/pt.cc                                  | 7 +++++++
 gcc/testsuite/g++.dg/modules/tpl-friend-8_a.H | 9 +++++++++
 gcc/testsuite/g++.dg/modules/tpl-friend-8_b.C | 8 ++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-friend-8_a.H
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-friend-8_b.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 5b9fc588a21..9e3085f3fa6 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -11448,6 +11448,13 @@ tsubst_friend_function (tree decl, tree args)
 	     by duplicate_decls.  */
 	  new_friend = old_decl;
 	}
+
+      /* We've just added a new namespace-scope entity to the purview without
+	 necessarily having opened the enclosing namespace, so make sure the
+	 enclosing namespace is in the purview now too.  */
+      if (TREE_CODE (DECL_CONTEXT (new_friend)) == NAMESPACE_DECL)
+	DECL_MODULE_PURVIEW_P (DECL_CONTEXT (new_friend))
+	  |= DECL_MODULE_PURVIEW_P (STRIP_TEMPLATE (new_friend));
     }
   else
     {
diff --git a/gcc/testsuite/g++.dg/modules/tpl-friend-8_a.H b/gcc/testsuite/g++.dg/modules/tpl-friend-8_a.H
new file mode 100644
index 00000000000..bd2290460b5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-friend-8_a.H
@@ -0,0 +1,9 @@
+// PR c++/100134
+// { dg-additional-options -fmodule-header }
+// { dg-module-cmi {} }
+
+namespace std {
+  template<class T> struct A {
+    friend void f(A) { }
+  };
+}
diff --git a/gcc/testsuite/g++.dg/modules/tpl-friend-8_b.C b/gcc/testsuite/g++.dg/modules/tpl-friend-8_b.C
new file mode 100644
index 00000000000..76d7447c2eb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-friend-8_b.C
@@ -0,0 +1,8 @@
+// PR c++/100134
+// { dg-additional-options -fmodules-ts }
+// { dg-module-cmi pr100134 }
+export module pr100134;
+
+import "tpl-friend-8_a.H";
+
+export std::A<int> a;
-- 
2.38.0.15.gbbe21b64a0